William was the son of James William Otis [1800-1869] and Martha Chursh Otis [d. 1888], and was the great-great-grandson of Harrison Gray [1711-1794]. Harrison Gray was the receiver-general for the Province of Masschusetts Bay from 1753 until the Revolution, and a sitter for a portrait by John Singleton Copley which is now in the NGA (1976.25.1). [Compiled from sources and references recorded on CMS]
Bibliography
1924
Otis, William A. A Genealogical and Historical Memoir of the Otis Family in America. Chicago, 1924: 341.